Apparatus for producing rod-shaped members of crystalline material

ABSTRACT

Combination in apparatus for producing rod-shaped members of crystalline material includes a sealed receptacle having a top wall, bottom wall and lateral wall portions, a pair of rod holders located in the receptacle substantially along the vertical central axis of the receptacle for supporting a rodshaped member of crystalline material therebetween, heating means mounted in the receptacle for producing a melting zone in the rod-shaped crystalline member, the heating means and the holders being displaceable relative to one another for passing the melting zone along the rod-shaped crystalline member, and drive means extending into the receptacle through a wall portion other than the bottom wall portion from a location outside the receptacle for moving the holders and the heating means relative to one another.

United States Patent [72] inventor Wolfgang Keller Pretzfeld, Germany [21] Appl. No. 871,783 [22] Filed Oct. 31, 1969 [45] Patented Nov. 16, 1971 [73] Assignee Siemens Aktiengesellschaft [32] Priority Sept. 9, 1965 [33] Germany [31] S 99 330 Continuation of application Ser. No. 578,088, Sept. 8, 1966, now abandoned. This application Oct. 31, 1969, Ser. No. 87 1 ,7 83

[ 5 4] APPARATUS FOR PRODUCING ROD-SHAPED MEMBERS OF CRYSTALLINE MATERIAL 5 Claims, 1 Drawing Fig.

[52] US. Cl. 23/273 SP, 23/301 SP [51] Int. Cl. B01j17/00 [50] Field of Search 23/273 SP, 301 SP, 295

[56] References Cited UNITED STATES PATENTS 2,809,905 10/1957 Davis et al. 23/273 Primary ExaminerNorman Yudkoff Assistant Examiner-R. T. Foster Attorneys-Curt M. Avery, Arthur E. Wilfond, Herbert L.

Lerner and Daniel J. Tick ABSTRACT: Combination in apparatus for producing rodshaped members of crystalline material includes a sealed receptacle having a top wall, bottom wall and lateral wall portions, a pair of rod holders located in the receptacle substantially along the vertical central axis of the receptacle for supporting a rod-shaped member of crystalline material therebetween, heating means mounted in the receptacle for producing a melting zone in the rod-shaped crystalline member, the heating means and the holders being displaceable relative to one another for passing the melting zone along the rod-shaped crystalline member, and drive means extending into the receptacle through a wall portion other than the bottom wall portion from a location outside the receptacle for moving the holders and the heating means relative to one another.

APPARATUS FOR PRODUCING ROD-SHAPED MEMBERS OF CRYSTALLINE MATERIAL This application is a continuation of Ser. No. 578,088, filed Sept. 8, 1966, now abandoned.

My invention relates to apparatus for producing rod-shaped members of crystalline material, and more particularly of semiconductive material such as silicon for example.

Apparatus of this type is exemplified by the equipment employed for carrying out crucible-free zone melting operations. During the crucible-free zone melting operation, a rod-shaped member of the material to be processed is usually clamped at both ends thereof and vertically supported in the apparatus. The holders which provide the support for the rod-shaped member are secured to vertically disposed shafts which can be continuously rotated about their axes. If the cross section of the rod-shaped member is to be altered during the zone melting operation, the holders can be suitablydisplaced in the vertical direction either toward or away from one another. A heating device is provided for producing a melting zone over a limited length of the rod-shaped member and, by moving the heating device and the rod-shaped member relative to one another, the melting zone can be passed through therodshaped member in the longitudinal direction thereof. The zone melting operation is performed generally for purifying the crystalline rod-shaped member or for growing monocrystalline rods with the aid of seed crystals fused to an end of the rod-shaped member. Since the crucible-free zone melting operation is conventionally carried out in a receptacle that is evacuated or filled with a protective gas, the shafts to which the rod holders are secured as well as a support or carrier for the heating device are inserted in such a way into the receptacle, which is either evacuated or filled with the protective gas, that the receptacle remains vacuumor gas-sealed, as the case may be. This is effected by providing suitable sealing retaining rings in the openings of the receptacle through which the aforementioned shafts and heating device carrier extend into the receptacle.

In another known method also performed in a receptacle that is evacuated or filled with a protective gas, crystalline material is heated in a crucible to a temperature above the melting point of the material. A seed crystal is then dipped into the melt and a rod-shaped member or body is pulled from themelt. Both the crucible and the seed crystal are secured at the ends of vertically extending shafts which are inserted into the receptacle through sealing retaining rings or washers which insure vacuumor gas-tightness of the receptacle. The shafts to which the crucible and the lower holder are secured are inserted from below into the receptacle of the cruciblefree zone melting apparatus. It has been found, however, that the retaining rings that are located at the bottom of the receptacle and through which the crucible bearing shaft the lower rod holder bearing shaft extend tend to become leaky even after a relatively short period of operation of the apparatus.

It has also been found that the premature wear of the retaining rings is caused by tiny fragments of the material being processed which split off from the recrystallizing rod during the pulling operation, drop to the bottom of the receptacle, and deposit between the retaining ring and the shaft extending therethrough, thereby damaging the retaining ring.

It is accordingly an object of my invention to provide apparatus for producing rod-shaped members of crystalline material wherein the receptacle thereof is provided with means for sealing the apparatus that are subjected to as little wear as possible. A further object of my invention resulting from the provision of sealing means subjected to minimal wear is to thereby provide apparatus which can function for relatively long periods without interruption or requiring servicing than has been heretofore possible with the known apparatusof this general type.

With the foregoing and other objects in view, I provide, in accordance with my invention, apparatus for producing rodshaped members of crystalline material, particularly semiconductive material such as silicon for example, comprising a sealed receptacle, a pair of rod holders located substantially along the vertical central axis of the receptacle for supporting a rod-shaped member of crystalline material therebetween, a heating device mounted in the receptacle for producing a melting zone in the rod-shaped member, the heating device and the holders being displaceable relative to one another for passing the melting zone along the rod-shaped member, and means for moving the holders and .the heating device, the moving means extending into the receptacle from a location above the rod-shaped member.

Other features which are considered as characteristic for the invention are set forth in the appended claims.

Although the invention is illustrated and described herein as embodied in apparatus for producing rod-shaped members of crystalline material, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.

The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of aspecific embodiment when read in'connection with the accompanying single figure of a drawing, in which there is shown diagrammatically an embodiment of the apparatus constructed in accordance with the invention.

Referring now to the drawing there is shown a receptacle 2 which is either evacuated or filled with a protective gas such as argon or nitrogen for example; a rod 3 of crystalline material is secured at its ends by holders 4 and 5 inside the receptacle 2. The holder 5 is secured to the end of a vertical shaft 6 which extends vacuum-sealed into the receptacle through a sealing retaining ring 7 disposed in the upper wall of the receptacle. The holder 4 is secured to the end of a shaft 8 which, if rotated so as to advantageously achieve more favorable results during a crucible-free zone melting operation, cannot however extend through the bottom wall of the receptacle 2, because otherwise the retaining ring located in the bottom wall would then tend to become defective and leak and thereby-have a deleterious effect upon the vacuum or gas atmosphere within the receptacle. Consequently, drive means for the holder shaft 8 are inserted from the top of the receptacle 2. The shaft 8 of the lower holder 4 is thus mounted in a carrier or support 9 rigidly connected to a vertically extending tube 10 which is closed at both of its ends and which projects upwardly out of the receptacle through a vacuumor gastight seal. A shaft 11 extends through the tube 10 and is provided with a chain drive 12 for driving the shaft 8 and the holder 4. A gas or vacuum tight connection is maintained between the shafts 11 and the lower closed end of the tube 10 by means of a sealing retaining ring or grommet 13 and is thereby protected against the wear produced by splitting off of particles from the processed material. If the cross section of the rod 3 is to be changed in the course of the zone-melting operation, as shown for example in the accompanying figure, the rod holders 4 and 5 must ;be displaced in a vertical direction relative to one another.

This displacement is effected by corresponding movement of the shafts 8 and 6, respectively, to which the rod holders are secured, as indicated by thedouble-headed arrows 14 and 15. Thus, for example, the holder 4 and its rotary shaft 8, can be moved vertically by suitably moving the tube 10 with the attached shaft carrier 9 by any suitable means.

It has also been known heretofore to provide uniform distribution of a doping material or dopant over the cross section of the recrystallizing rod by laterally or horizontally displacing the axis of the recrystallized rod portion so that it is offset with respect to the axis of the rod portion being supplied to the melt or, in other words, the original rod portion. The distribution of dopant can be made even more uniform by continually shifting the rod portion axis relative to one another in varying directions during the zone melting operation. With the apparatus constructed in accordance with my invention, the tube 10 can be turned about its vertical axis through small rotary angles in clockwise and counterclockwise directions to provide this necessary movement for achieving greater uniformity of the dopant distribution. A heating device which consists for example of an induction coil 16 energized by high-frequency current produces a melting zone 18 in the rod 3. The induction coil 16, which may be cooled by a suitable coolant liquid, is secured to a rod-shaped carrier 17 which consists of two electrically conductive coaxial tubes, the outer one thereof being usually connected at ground potential. The outer surface of the inner tube of the coil carrier 17 is advantageously covered with an insulating layer and is connected to the voltage-carrying end of a high-frequency source (not shown). The coil 16 can have a hollow tubular construction and can be so connected to the inner and outer tubes of the carrier 17 that the cooling liquid can be supplied thereto through the inner tube of the carrier 17 and discharged therefrom through the space between the outer tube and a steel tube coaxial to and surrounding the same (not shown). The heating coil 16 can be displaced along the rod 3 by suitably shifting the coil carrier 17 in a vertical direction upwardly or downwardly as indicated by the double headedarrow 19. A sealing retaining ring 20 is provided in an opening through the upper wall of the receptacle 2 to permit vacuumtight extension of the heating coil carrier rod 17 into the receptacle 2.

The shaft 8 and its bearing, as well asthe retaining ring 13 and the chain drive 12, are prevented from being damaged by the heat produced from the melting zone 18, by the fact that the carrier 9, which extends substantially at right angles from the tube 10, can be cooled particularly, for example, by means of a cooling loop 21 consisting of a tube 22 through which a coolant liquid is supplied and the tube proper through which the coolant is then returned to a location outside of the receptacle 2 and discharged as indicated by the associated arrows in the figure. The shaft 11 extends through the ends of the tube 10 whose interior is sealed from the inner chamber of the receptacle 2 by means of sealing retaining rings or grommets l3 and 23. The driving mechanism located outside the receptacle correspond to the known apparatus for carrying out crucible-free zone melting operations such as is described for example in U.S. Pat. No. 3,030,194 to R. Emeis, U.S. Pat. No. 3,160,478 to T. Rummel et al., and in my copending application Ser. No. 563,301, filed July 6, l966, now U.S. Pat. N 0. 3,351,433, all of which are assigned to the assignee of the instant application.

In the case where the invention of the instant application is to be employed for producing semiconductor rods by pulling from a crucible, the crucible is secured in the lower holder 4. The crucible and the heating device surrounding it are not displaced relative to one another; therefore the conductors or leads to the heating device can be passed through the tube 10 into the receptacle.

1 claim:

1. ln apparatus for producing rod-shaped members of crystalline material, the combination'of a sealed receptacle having a top wall, bottom wall and lateral wall portions, a pair of rod holders located in said receptacle substantially along the vertical central axis of said receptacle for supporting a rod-shaped member of crystalline material therebetween, heating means mounted in said receptacle for producing a melting zone in the rod-shaped crystalline member, said heating means and said holders being displaceable relative to one another for passing the melting zone along the rod-shaped crystalline member, drive means comprising separate drives for said pair of rod holders, respectively, extending into said receptacle through said top wall portion from a location outside the receptacle for moving said holders and said heating means relative to one another, the lower one of said rod holders being secured to the upper end of a vertical shaft, and a tubular member extending downwardly into said receptacle and having a carrier member at the lower end thereof extending transversely to and rotatably supporting said shaft, said tubular member being rotatable about its vertical axis.

2. In apparatus for producing rod-shaped members of crystalline material, the combination of a sealed receptacle having a top wall, bottom wall and lateral wall portions, a pair of rod holders located in said receptacle substantially along the vertical central axis of said receptacle for supporting a rod-shaped member of crystalline material therebetween, heating means mounted in said receptacle for producing a melting zone in the rod-shaped crystalline member, said heating means and said holders being displaceable relative to one another for passing the melting zone along the rod-shaped crystalline member, drive means comprising separate drives for said pair of rod holders, respectively, extending into said receptacle through said top wall portion from a location outside the receptacle for moving said holders and said heating means relative to one another, the lower one of said rod hol ders being secured to the upper end of a vertical shaft, a tubular member extending downwardly into said receptacle and having a carrier member at the lower end thereof extending transversely to and rotatably supporting said shaft, and means for cooling said carrier member.

3. Apparatus according to claim 5, wherein said cooling means comprises a cooling loop surrounding said carrier member.

Apparatus according to claim 5, wherein said tubular member contains another tube, said tubular member and said other tube comprising supply and discharge members for coolant to and from said cooling means.

5. ln apparatus for producing rod-shaped members of crystalline material, the combination of a sealed receptacle having a top wall, bottom wall and lateral wall portions, a pair of rod holders located in said receptacle substantially along the vertical central axis of said receptacle for supporting a rod-shaped member of crystalline material therebetween, heating means mounted in said receptacle for producing a melting zone in the rod-shaped crystalline member, said heating means and said holders being displaceable relative to one another for passing the melting zone along the rod-shaped crystalline member, drive means comprising separate drives for said pair of rod holders, respectively, extending into said receptacle through said top wall portion from a location outside the receptacle for moving said holders and said heating means relative to one another, the lower one of said rod holders being secured to the upper end of a vertical shaft, a tubular member extending downwardly into said receptacle and having a carrier member at the lower end thereof extending I transversely to and rotatably supporting said shaft, said drive for said lower rod holder including another shaft extending through said tubular member into said receptacle, and substantially horizontally extending power transmission means operatively interconnecting said other shaft and said shaft to which said lower holder is secured whereby said latter shaft is rotatable by rotation of said other shaft, said other shaft being located in said vertical tubular member and said vertical tubular member being rotatable in either rotary direction for turning said shaft to which the lower holder is secured in said rotary directions relative to said upper holder.

* l l l III 

2. In apparatus for producing rod-shaped members of crystalline material, the combination of a sealed receptacle having a top wall, bottom wall and lateral wall portions, a pair of rod holders located in said receptacle substantially along the vertical central axis of said receptacle for supporting a rod-shaped member of crystalline material therebetween, heating means mounted in said receptacle for producing a melting zone in the rod-shaped crystalline member, said heating means and said holders being displaceable relative to one another for passing the melting zone along the rod-shaped crystalline member, drive means comprising separate drives for said pair of rod holders, respectively, extending into said receptacle through said top wall portion from a location outside the receptacle for moving said holders and said heating means relative to one another, the lower one of said rod holders being secured to the upper end of a vertical shaft, a tubular member extending downwardly into said receptacle and having a carrier member at the lower end thereof extending transversely to and rotatably supporting said shaft, and means for cooling said carrier member.
 3. Apparatus according to claim 5, wherein said cooling means comprises a cooling loop surrounding said carrier member.
 4. Apparatus according to claim 5, wherein said tubular member contains another tube, said tubular member and said other tube comprising supply and discharge members for coolant to and from said cooling means.
 5. In apparatus for producing rod-shaped members of crystalline material, the combination of a sealed receptacle having a top wall, bottom wall and lateral wall portions, a pair of rod holdeRs located in said receptacle substantially along the vertical central axis of said receptacle for supporting a rod-shaped member of crystalline material therebetween, heating means mounted in said receptacle for producing a melting zone in the rod-shaped crystalline member, said heating means and said holders being displaceable relative to one another for passing the melting zone along the rod-shaped crystalline member, drive means comprising separate drives for said pair of rod holders, respectively, extending into said receptacle through said top wall portion from a location outside the receptacle for moving said holders and said heating means relative to one another, the lower one of said rod holders being secured to the upper end of a vertical shaft, a tubular member extending downwardly into said receptacle and having a carrier member at the lower end thereof extending transversely to and rotatably supporting said shaft, said drive for said lower rod holder including another shaft extending through said tubular member into said receptacle, and substantially horizontally extending power transmission means operatively interconnecting said other shaft and said shaft to which said lower holder is secured whereby said latter shaft is rotatable by rotation of said other shaft, said other shaft being located in said vertical tubular member and said vertical tubular member being rotatable in either rotary direction for turning said shaft to which the lower holder is secured in said rotary directions relative to said upper holder. 